There used to be a penalty for voluntary tackle ... hold on there still is. Atkins is just a cheat.
I don't think people quite know what voluntary tackle is.
Voluntary tackle isn't about falling to the ground or staying on the ground with no one touching you. That has been around since 1908.
The voluntary part is playing the ball. Playing the ball when before a tackle is complete, or before a ref calls hold, immediately puts everyone off side. By 'voluntary' playing the ball before the tackle is completed you've given your team an unfair advantage.
Thats why it's not a voluntary tackle just for chucking yourself at the ground. In that case fullbacks and wingers diving for the infield from in goal would always be penalised. Or wingers close to the sideline. Props who are doing settlers close to the line and are almost flopping to get that fast play the ball would be the same.
Voluntary tackles is around the play the ball and 'completing the tackle' unfairly, not about playing dead in tackles or staying on the ground